“Each Additional Half-Degree Counts for the Climate”
The climate is warming, but there is still time to act: this is the message being repeated by the paleoclimatologist Valérie Masson-Delmotte, prior to COP24 held in Poland from 3rd to 14th December. Her role in the IPCC makes her one of France’s leading figures in sharing knowledge about climate change.
Photo © Bruno Lévy
Valérie Masson-Delmotte is one of a group of world experts on global warming. On 7th October 2015, she was elected joint chair of Working Group 1 (devoted to climate physics) on the Intergovernmental Panel on Climate Change (IPCC). In this capacity, she coordinated the writing of the special report on 1.5°C limit to global warming, published on 8th October 2018. At the Climate Science Laboratory in Saclay, she is also working on ice cores and, with her colleagues, has reconstituted more than 800,000 years of climate history. Analysis of samples of ancient atmosphere contained in bubbles of air in the ice show the rupture corresponding to the profound upheaval in atmospheric composition and the increase in the greenhouse effect due to human activities. Valérie Masson-Delmotte is committed to ensuring that scientific facts are used for decision-making, at all levels.
La Recherche • With the IPCC, you have just published a special report on the consequences of global warming by 1.5°C. How did it come about?
Valérie Masson-Delmotte • The IPCC’s mandate is to make assessments of the state of relevant scientific knowledge to enlighten political decisions, the themes of which are decided during plenary sessions of representatives from 195 countries. In the Decision of COP21, held in Paris in December 2015, the United Nations Framework Convention on Climate Change invited us to make this report on global warming by 1.5°C; an invitation that we accepted during the IPCC plenary session in Kenya in April 2016. The initial request concerned the impacts of global warming of 1.5°C and the greenhouse gas pathways compatible with such stabilization. It was made by the most vulnerable countries, for whom the Paris Agreement target (limiting warming well below 2°C) was not ambitious enough to contain the climate risks. In 2015, the scientific knowledge about these aspects was poor. The IPCC then decided to include this report within the context of a stronger global response to the threat of climate change (i.e. adaptation and mitigation), sustainable development and eradicating poverty, which is the United Nation’s primary Sustainable Development Goal. This decision anchors the requested assessment in the multiple dimensions of sustainability, with a strong social dimension. This framing makes the report quite innovative. It was finally approved at the October plenary session held in Incheon in South Korea, following a Herculean task by the authors and over 100 hours of discussions! What were its major conclusions? After closely examining more than 6,000 studies, three quarters of which were published after 2014, we were astounded to note how much each additional half-degree counts. Human activities have already caused approximately a 1°C increase since the pre-industrial period (1850-1900), the effects of which are already being felt on ecosystems and living conditions. This human-caused warming is continuing at a current rate of 0.2°C per decade. At this speed, we will reach 1.5°C between 2030 and 2050!
What are the differences between a world that is 1.5°C warmer and 2°C warmer?
There are very clear regional differences in the average warming on land and at sea, statistical changes in extreme events, i.e. heatwaves in all inhabited regions, torrential rains or episodes of drought in some regions, such as the Mediterranean. With an additional 1.5°C, 70 to 90% of coral reefs will be severely damaged, compared to 99% for 2°C; 6% of insects, 8% of plants and 4% of vertebrates risk losing more than half of their natural habitat at 1.5°C compared to respectively 18%, 16% and 8% with a 2°C increase. For the Arctic permafrost, which is thawing due to warming, maintaining 1.5°C would preserve 1.5 to 2.5 million square kilometres compared to 2°C. In any case, sea levels will continue to rise, but limiting warming to 1.5°C would reduce the rise by 10 cm compared to warming by 2°C, and would therefore allow more time for coastal regions to adapt. For populations, this half-degree difference would represent 10 million fewer people exposed to the risks of rising sea levels and half as many would suffer from lack of water. You need to remember that a 1.5°C average increase does not mean 1.5°C everywhere. 1.5°C more, could mean 3°C more during heatwaves, without taking account of the amplifying effect of urban heat islands.
Are there regions that are more vulnerable?
The risks are disproportionately higher for regions of the Arctic, semi-arid dry zones and for small-island developing States, because the consequences of the warming are more intense, or because they are more vulnerable or because these regions are more exposed to cumulative effects. For example, rising sea levels, increased groundwater salinity, more episodes of torrential rain, damage to coral reefs and reduced fishing resources are compound risks for these small insular States.
How much time do we have to act before it is too late?
Reaching the goal of 1.5°C is not unrealistic geophysically; it all depends on the pathway of future greenhouse gas emissions, and on unprecedented systemic transitions. Stabilising warming at 1.5°C would require reducing emissions of CO2 (the main greenhouse gas) by 45% in 2030 compared to 2010 levels, and in 2050, net zero CO2 (meaning we emit as much CO2 as we extract from the atmosphere for long-term storage), and a 30% drop in methane and other compounds, such as black carbon. For most of the pathways assessed, it also means reaching negative CO2 emissions to offset emissions from sectors where carbon is more difficult to remove, such as transport and agriculture. Every year, 42 billion tonnes of CO2 are released into the atmosphere. What counts for the peak in global warming is the past, present and future cumulative net CO2 emissions, and the net effect on the climate of other compounds emitted by human activities. The longer we wait, the higher the cumulative CO2, and inevitably, the higher the level at which the climate will stabilize: every year counts. A second thing needs to be taken into consideration: the effect on the climate of other greenhouse gases such as methane, nitrous oxide or particles of pollution. Acting on these compounds is also necessary to limit the intensity of the peak in temperature, with potentially considerable benefits in improved air quality and public health.
What options do we have to meet this target?
The IPCC report deals with these options in the form of pathways, which reflect very different political choices, modes of development, changes in behaviour and technological options. There are a multitude of pathways, but they all require transitions of major energy systems, urban and industrial systems, land management (agriculture, forestry and food) and finally, infrastructures. These transitions are based on redirecting some investment and in particular, on multiplying investment in low-carbon options and energy efficiency by five by the year 2050. Some aspects are common to all pathways: very rapid reduction in the use of coal to produce electricity, 50 to 85% of electricity from renewable sources by the year 2050. Finally, one of the originalities of the report is assessing the enabling conditions for deployment of each adaptation or mitigation option for the major systems transitions by means of six dimensions of feasibility (geophysical, environmental, technological, economic, socio-cultural and institutional). This analysis identifies the measures that can be taken in the short term and enables barriers to be overcome to enable other harder options to be deployed.
How can CO2 in the atmosphere be reduced?
To extract CO2 from the atmosphere, there is a whole range of different options: afforestation or reforestation, restoration of damaged ecosystems, farming practices that store carbon lastingly in the soil, direct CO2 capture from the air using physical-chemical processes. Or, on a much larger scale, the use of bioenergy (*). Each of these options has potential, but also limits that we have highlighted in our report. After publication of the report, some showed a certain fatalism and a feeling of powerlessness that does not reflect its content. Indeed, our report focuses on new knowledge about the risks associated with a half degree more and shows that it is not inevitable that we will exceed 1.5°C or more, from a geophysical point of view. Everything depends on our ability to facilitate the deployment of solutions and these system transitions. We show the potential of measures at all levels (international or national institutions, regions, individual choices) and for all stakeholders in society. I believe this report underlines how much our choices count, by clearly showing that we are at the crossroads of three major risks. The first is entering a world in which the climate continues to heat up (1.5°C or more), where the most fragile ecosystems and societies will gradually crack and where we will have to manage crisis upon crisis. The second risk is the weight we will be imposing on younger generations if we don’t act now; they will have to adapt to a more rapidly changing climate. To control it, they will have to act more brutally to reduce greenhouse gas emissions or deploy very risky measures to extract CO2 from the atmosphere on a large scale and store it sustainably. The final risk is that of transition that is (too) fast for our economic and financial systems. Which risks are we willing to take?
Today, the finger is often pointed at China and the United States as the largest emitters of CO2. Is that true?
It all depends on how emissions are counted; the historical cumulative for each country, current emissions or emission per inhabitant. The European Union and the United States have obvious historical responsibility. Currently, the three biggest emitters are the United States (around 16 tonnes of CO2 per year per inhabitant), the European Union (7) and China (also 7). In around fifty countries, CO2 emissions have already passed their peak and are falling, as in Europe since 1990 and in the United States since 2005. In China, emissions have levelled off over the last few years. Significant efforts are being made in this country to master and reduce the proportion of coal in energy production, to enhance air quality and reduce emissions, with major investment in low-carbon electricity production and electrification of transport. In the United States, greenhouse gas emissions have been falling continuously since 2005. However, since Donald Trump was elected, there has been clear environmental deregulation to eliminate laws previously implemented to improve energy efficiency, control greenhouse gas emissions and protect ecosystems. At the same time, many American states and cities are actively involved in reducing their greenhouse gas emissions and improving their air quality, like in California.
What is the situation in France?
Greenhouse gas emissions have stopped falling and have even been rising for three years. We are behind on most of our greenhouse gas emission targets, be it for transport, construction or farming. It would be interesting to analyse the reason for these delays in implementing effective policies, by looking at successful transitions in other European countries. Recent events have also shown how unprepared we are for the current climate and its variability. We only need to see the tragic consequences of the torrential rain that fell in October 2018 in the south of France, the hurricanes in our overseas territories or the persistent drought that occurred also in 2018. If we continue like this, we will end up in a permanent situation of crisis. However, I have noted a sort of velvet citizen’s revolution. Society expects it. In October 2018, students from HEC Paris, AgroParisTech, CentraleSupélec, École Polytechnique and ENS Paris started a manifest entitled “For an Ecological Awakening“, which has since been signed by over 20,000 students from a dozen different schools. There is a considerable gap between most politicians and citizens. You are a paleoclimatologist, meaning you study ancient climates, using ice cores. What lessons do you learn to interpret our current climate? When studying the ice in Greenland, we reconstituted 130,000 years of local climate history, and quantified the amplitude and speed of temperature changes in Greenland using several methods. For the Antarctic, our records of changes in the atmospheric composition and in local temperature reveal variations over the last 800,000 years. These data show the disruption associated with the industrial revolution and the profound and rapid change in the atmospheric composition due to our greenhouse gas emissions. They also underline the vulnerability of ice caps to polar warming just a few degrees above pre-industrial levels and highlight an amplification in temperature variations at the polar regions. We showed that the fastest temperature changes on the surface of the Earth occurred at the end of ice ages, with amplitudes of the order of 5°C and a maximum speed of about 1°C per millennium. If we look at periods more comparable to ours, warm periods therefore, the current warming constitutes a break from the variations of the last two millennia. For a few decades, we have been coming out of the range of temperature variations in the current interglacial period, the Holocene, with an average temperature on the surface of the Earth which has been relatively stable for 11,700 years (despite regional variations). Currently for example, the CO2 content in the atmosphere is 400 parts per million (ppm), a concentration not reached since the Pliocene, 3 million years ago. Warms periods during the Pliocene were 2 to 4°C hotter than 19th century temperatures, and the sea levels were 10 to 20 m higher…
How are these data from past climates used?
They are used to assess the ability of our digital climate models to represent very different climates from those we have today. They also serve to understand the natural variability of the climate and how it responds to various disturbances. We have noted that climate models are able to represent the major traits of past changes correctly, but with a tendency to underestimate the amplitudes of some variations. Furthermore, observed characteristics of temperature changes over the last thirty years confirm the validity of the first projections of the climate’s response to added greenhouse gases in the 1980s. Today, the stability of our societies depends on our ability to master climatic risks.
(*) Bioenergy with the capture and storage of carbon is a technique that consists of growing plants or trees that capture CO2, and burning them to produce energy, recover the CO2 emitted by combustion and sequestering it in the soil.
TWO SCENARIOS FOR THE ANTARCTIC AND SOUTHERN OCEAN In a study published in June 2018, the authors (including Valérie Masson-Delmotte) stepped into the shoes of an observer in 2070 and looked back at what had happened over the previous fifty years. They imagined two scenarios: one with high greenhouse gas emissions and the other with reduced emissions. In the first scenario, the Antarctic and the Southern Ocean had completely changed in appearance; it was 3°C warmer in the Antarctic, the temperature of the Southern Ocean had increased by 1.9°C, floating ice platforms had diminished by 23% and the contribution to the rise in sea levels was 27 cm. The number of invasive species had grown tenfold and the ecosystems had completely changed. Reduced emissions led to a 0.9°C temperature increase in the Antarctic, and the changes were controlled and less significant: the ice platforms had “only” lost 8% of their surface area, for a contribution of “only” 6 cm to rising sea levels. The temperature of the Southern Ocean was “only” 0.7°C higher. Finally, ecosystems were less affected; for example, invasive species had “only” doubled.
> INTERVIEWEE
Valérie Masson -Delmotte
Paleoclimatologist at INRA, at the Climate Science Laboratory in Saclay, she is one of a group of world experts on global warming and is committed to ensuring that scientific facts are used for decision-making, at all levels.
1996 • Following her thesis at the École Centrale de Paris, in fluid physics and transfers, she became a research scientist at the CEA. 1998-2008 • She became head of the Glaccios team in the Climate and Environment Sciences Laboratory (LSCE), in Saclay. Since 2008 • she has been director of Research at the CEA. 2013 • She won the Irène Joliot-Curie prize for Science Woman of the Year. Since 2005 • she has co-chaired Working Group 1 of the IPCC (which studies the physical bases for the climate).
